Acanthurus sandvicensis
Spot Hawaiian Convict Surgeonfish in Hawaii, the Maldives, and the Philippines. Best sightings Oct, Apr in the Northern Hemisphere. ID tips and top dive sites inside.
Bold vertical black-and-white bars running across the body are the standout feature, the 'convict' stripes that give this fish its name. At around 18 cm it sits comfortably in the mid-range surgeonfish size bracket, with the oval, laterally compressed body shape typical of the family. Look for the small but sharp caudal spine (a retractable blade near the tail base) characteristic of all surgeonfish. Juveniles share the same striped pattern as adults, making them easy to identify at any size.
You'll usually come across these fish busy grazing algae off hard reef substrate, they rarely stop moving. They're relaxed around divers and won't bolt, but pay attention during feeding: they can get snappy with other fish that crowd their patch, and that competitive energy can make a school feel surprisingly lively. Early morning and late afternoon are worth targeting, when feeding activity tends to peak.
As algae grazers working in groups, Hawaiian Convict Surgeonfish act as living lawn-mowers for the reef, their constant cropping keeps algae from smothering coral, which makes healthy populations a good sign of reef condition.
In Northern Hemisphere destinations such as Hawaii, sightings concentrate from October through April. Across tropical Indo-Pacific sites closer to the equator, water temperatures stay within the species' preferred range of roughly 22-29 °C year-round, so encounters are possible in any month.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Hawaii is by far the strongest region for reliable sightings, which makes sense given the species name. Beyond Hawaii, divers also log it regularly across the Maldives, the Philippines (particularly the Visayas and Palawan), and Bali and Lombok in Indonesia. Australia's Queensland coast also has solid records.
Mapping where Hawaiian Convict Surgeonfish is logged…
Hawaii is the most reliable destination, given the species' name and strong sighting records there. They're also logged across the Maldives, the Philippines (Visayas, Palawan), Indonesia (Bali, Lombok), and Queensland, Australia. Despite the Hawaiian name, the species has a broad Indo-Pacific range.
In Hawaii and other Northern Hemisphere sites, sightings peak from October through April. In equatorial regions like the Maldives and Indonesia, the water stays warm enough year-round for the species to be present, so timing matters less there.
Look for the striking vertical black-and-white stripes, the convict pattern is the giveaway. The body is oval and compressed, typical of surgeonfish, and the fish is modest in size at around 18 cm. Both juveniles and adults share the same striped look, so size is the only variable.
They typically reach around 18 cm, roughly the length of a hand. That puts them on the smaller side compared to some surgeonfish relatives, but in a feeding school they can still make a strong visual impression.
No. They're relaxed around divers and pose no real threat. Like all surgeonfish they carry a sharp spine near the tail base, but it's a defence used against other fish rather than people. Keep a reasonable distance and you'll have no issues.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Striped Surgeonfish
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